1. Field of the Invention
The present invention relates to an image formation apparatus and, more particularly, to an image formation apparatus for forming breast images on a recording medium based on breast image data acquired by mammography.
2. Description of the Related Art
In an examination of breast cancers, mammographic images of left and right breasts which are acquired mammographically and formed on a thermally developed photosensitive material are arrayed side by side and compared for diagnosis. Such a mammographic image is obtained by producing breast image data by a mammography imaging unit, sending the data to an image formation apparatus, and optically exposing and thermally developing the image to visualize it. In the mammography imaging unit, image data are generally treated as follows to facilitate doctor's diagnosis. One of the left and right breast images is rotated through 180° such that the left and right breast images are placed in a back to back relation about the chest walls. Then, the image data are output.
A known image output processing apparatus for forming such mammographic images consists of forming breast images on a thermally developed photosensitive material, placing the images such that they do not touch the front or rear end of the photosensitive material in the direction of transportation or placing the images of the left and right breasts in a back to back relation about the chest wall portions, and outputting the images with optimum layout (see, for example, JP-A-2004-138786).
With this image output processing apparatus, when a thermally developed photosensitive material is brought into contact with the heat application portion of the thermal development portion and developed, images of breasts are so placed that they are not formed at the front end or rear end of the thermally developed photosensitive material in the direction of transportation; otherwise, the transfer of heat from the heat application portion would become unstable, tending to cause a decrease of the concentration of the mammographic images or nonuniformity of the concentration. In this way, the effects of the concentration nonuniformity on the diagnosis are suppressed.
As described previously, the image output processing apparatus of JP-A-2004-138786 suppresses decrease and nonuniformity of the concentration of mammographic images in the direction of transportation of the thermally developed photosensitive material. However, decrease and nonuniformity of the concentration also take place in the widthwise direction perpendicular to the direction of transportation of the thermally developed photosensitive material.
In particular, each mammographic image formed on the thermally developed photosensitive material is visualized by bringing the photosensitive material into contact with the heating portion of the thermal development portion. The photosensitive material has been optically exposed by the image exposure portion and a latent image has been formed on the photosensitive material. Thus, a visible image is formed. Considerations are given to the temperature distribution of the heating portion such that the thermally developed photosensitive material is uniform in temperature in order to heat every portion of the photosensitive material with uniform temperature. However, as shown in FIG. 10A, a larger amount of heat is dissipated from each end of the heating portion than from the center. The temperature at each end tends to drop.
When a thermally developed photosensitive material is brought into contact with the heating portion having a temperature distribution in the widthwise direction as described above and development is done, there is the danger that the concentration becomes nonuniform across the width of the thermally developed photosensitive material. That is, as shown in FIGS. 10B and 10C, where the images to be developed are mammographic images, if an image A of the right breast and an image 8 of the left breast are output separately, then a mammographic image 11 to be developed which is obtained from the image A by making contact with the center of the heating portion (i.e., the heating portion of uniform temperature) is developed with desired temperature. As a result, normal concentration is obtained. On the other hand, a mammographic image 13 which is to be developed and is obtained from the image B by making contact with ends of the heating portion that tend to drop in temperature is developed with lower temperature. Consequently, there is the possibility that normal concentration is not obtained.
More particularly, each point, for example, on a line a constituting the breast image A of the mammographic image 11 is brought into contact with the heating portion of given temperature TB and developed. Meanwhile, each point on a line b on the breast image B that is in a position corresponding to the line a of the breast image A is brought into contact with the heating portion of lower temperature Tb and developed. Accordingly, there is the danger that comparison of corresponding portions of the breast images A and B (e.g. points PR and PL) in terms of concentration and hue reveals that these portions are different in concentration and hue. Since alphanumeric information is formed in ancillary relationship to the mammographic images 11 and 13, the up-down direction of the mammographic images 11 and 13 can be discerned during outputting. In this example, for the sake of convenience, arrows are attached to the mammographic images 11 and 13, and the direction indicated by the arrows is defined as the upward direction in the figure.
The mammographic images 11 and 13 obtained in this way are arranged such that the chest wall portions AK and BK of the breast images A and B are placed in a back to back relation as shown in FIG. 11. Then, the images are placed on a showcase. The doctor observes the images A and B of the left and right breasts (mammographic images 11 and 13), discerns subtle differences in geometry and concentration between both breasts, and makes a diagnosis. However, as described previously, the corresponding portions of the breast images A and B are brought into contact with heating portions of different temperatures and developed. Consequently, they may differ in concentration and hue. There is the possibility that it is less easy for the doctor to make a diagnosis.
Accordingly, there is a demand for further improvement to prevent nonuniformity of concentration and hue in the widthwise direction of a thermally developed photosensitive material, in addition to the direction of transportation, in order to obtain mammographic images of good quality (i.e., uniform in concentration and hue over the whole surface of each mammographic image).